Portion of a chair back



FIG. 1 is an isometric view of a portion of a chair back showing my new design.

FIG. 2 is a front view thereof.

FIG. 3 is a top view thereof.

FIG. 4 is a bottom view thereof.

FIG. 5 is a right side view thereof; and,

FIG. 6 is a left side view thereof.

The broken lines shown in FIGS. 1-6 are included for the purpose of illustrating environmental elements only and form no part of the claimed design. The dotted line shown in FIGS. 1-3 and 5-6 represents an unclaimed border between claimed and unclaimed subject matter forms no part of the claimed design. The rear view is omitted and forms no part of the claimed design. 

The ornamental design for a portion of a chair back, as shown and described. 